The present invention relates to a self-adapting method of controlling the mixture ratio of an internal combustion engine injection system.
As is known, the injection systems of many currently marketed vehicles feature a mixture ratio control system based on a self-adapting strategy designed to ensure supply of the amount of fuel required to obtain an exhaust ratio equal to an objective ratio, to compensate for any production differences causing the engine and injection system to deviate from the nominal on which the settings are based, to compensate for in-life component drift and ageing which might affect the control system, and to supply useful information concerning the state of the components with a view to diagnosing the injection system.
Currently used self-adapting algorithms are based on the assumption that any differences or malfunction which might affect correct preparation of the air/fuel mixture can be traced to an error in the injector actuation characteristic defined by the relationship between injection time and the amount of fuel injected.
In the injection central control unit, the above characteristic is approximated by a line defined by two parameters: gain and offset, i.e. by the slope and initial value with respect to a predetermined reference system.
According to the above self-adapting algorithms, errors due to production variations and ageing can be traced to errors in estimating the set gain and offset.
The adaptive gain and offset parameters are applied in all engine operating conditions, except for start-up, and are only updated in steady operating conditions of the engine.
The two adaptive parameters are not updated simultaneously, but according to a precise operating sequence. That is, keeping the gain value fixed, offset updating is enabled within a particular stabilized-engine window close to the idling condition; once offset is updated, the gain value is corrected in another stabilized-engine window corresponding to a high speed and load situation; and the sequence is repeated to obtain a real value by successive approximations.
Though widely used in the automotive industry, the above strategy has the major drawback of being intrinsically very slow in adapting.
It is an object of the present invention to provide a self-adapting mixture ratio control method designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a self-adapting method of controlling the mixture ratio of an injection system, of an internal combustion engine, comprising a number of injectors, each for injecting a respective operating quantity of fuel at each engine cycle; and a stoichiometric composition sensor generating a composition signal related to the stoichiometric composition of the exhaust gases produced by said engine; in each operating state of the engine and for each said injector, said method comprising the steps of:
a) determining a nominal quantity of fuel to be injected;
b) determining an operating parameter as a function of said composition signal and of a proportional-integral regulating function; characterized by also comprising the steps of:
c) determining a current hot correction coefficient indicating a correction to be made to said nominal quantity of fuel to take into account the effect on injection of differences of different engines and of said injection systems thereof upon the engine reaching normal operating temperatures; and
d) determining said operating quantity of fuel to be injected as a function of said nominal quantity, of said operating parameter, and of said current hot correction coefficient.